The invention relates to breathing equipment for high altitude flights, above about 15,000 meters.
In order to protect the crew members of high altitude flying planes against risks of anoxia and air embolism, the following solution is generally adopted in present military aircraft; from about 1,500 meters, there is established in the living space an over-pressure with respect to the surrounding atmosphere, this over-pressure increasing with the altitude to reach 300 millibars at about 5,000 meters and then remaining constant. A breathing gas regulator is provided which supplies individual breathing masks, from an oxygen supply, at first with oxygen diluted with ambient air drawn from the cabin, then with pure oxygen to supply to the personnel a breathing mixture at an acceptable partial oxygen pressure.
In the case of loss of cabin pressure or ejection, the crew members become subjected to the surrounding atmospheric pressure. Equipment must be provided for then modifying the breathing gas supplied to the breathing equipment so as to avoid any loss of consciousness during the time necessary to reach a "safe" altitude (about 9,000 meters) from the highest possible flight altitude.
In the case of flights not exceeding 15,000 meters, it is sufficient to provide a regulator supplying the personnel with pure pressurized oxygen in case of accident. For very high altitude flights, the only sure solution at present consists of using a total pressurisation helmet enclosing the head and the neck of the crew member, associated with a pneumatically pressurised garment. Such equipment provides for a stay at 30,000 meters for periods which do not substantially exceed one hour. But it has numerous disadvantages. The helmet is heavy, all the more so since it must be sufficiently rigid to withstand the internal pressure. It must be strapped to the body of the wearer for resisting the forces due to the pressure which prevails inside it and tends to snatch it away. The eye-piece, being sealingly closed during the whole flight, hinders the pilot.
On the other hand, present non-pressurised helmet equipment, even if better tolerated for normal flights, does not provide a sufficient protection beyond about 15,000 meters. To prevent the personnel from losing consciousness, it is necessary to supply the helmet with oxygen at an over-pressure in relation to the ambient atmosphere, such that it causes serious troubles and particularly: accidents to the internal ear; an oxygen flow via the tear ducts, which disturbs the vision; and swelling of the neck.
It is an object of the invention to provide breathing equipment which protects the wearer against loss of pressurisation of the space in which he lives at high altitudes, for a period of time sufficient for him to regain a safe altitude from the highest flight altitude and does not present the disadvantages of a total pressurisation helmet.
According to an aspect of the invention, there is provided breathing equipment comprising a breathing mask constructed to supply breathing gas under pressure and a helmet provided with means which, responsive to supply of the mask with breathing gas at an over-pressure greater than a threshold, subject only the more sensitive organ(s) of the head to a gas over-pressure not exceeding that which prevails in the mask. The over-pressure(s) may increase from a few millibars up to a value which reaches several tens of millibars at an altitude of 20,000 meters and above.
Such equipment permits the differential oxygen pressures applied to the sensitive organs to be limited to physiologically acceptable values. The values associated with different organs may be different: e.g. a greater differential pressure can be accepted for the eyes than for the ears.
In accordance with a particular feature of the invention, the helmet is provided with ear-pieces tightly applied against the head and defining around each ear a compartment provided with a pipe for bringing gas from the mask supply, comprising flow limiting means, such as a restriction, and a calibrated valve which limits the over-pressure.
According to another optional feature of the invention, the equipment comprises an eye-piece or goggles which, when placed in front of the eyes, define around the eyes a chamber provided with a pipe for bringing the gas from the mask supply, comprising a flow limiting restricted orifice and a calibrated valve which limits the over-pressure.
The calibrated valves may be designed not only to limit the over-pressure, but also to avoid oxygen losses by sealing the system tight in normal conditions of use.
The invention will be better understood after reading the following description of particular embodiments given as non-limiting examples.